This invention relates in general to photography and in particular to improved black-and-white developing compositions. More particularly, it relates to improved and stabilized ascorbic acid developing compositions and to methods for their use in processing photographic silver halide materials.
Photographic black-and-white developing compositions containing a silver halide black-and-white developing agent are well known in the photographic art for reducing silver halide grains containing a latent image to yield a developed photographic image. Many useful developing agents are known in the art, with hydroquinone and similar dihydroxybenzene compounds and ascorbic acid (and derivatives) being some of the most common. Such compositions generally contain other components such as sulfites, buffers, antifoggants, halides and hardeners.
Dihydroxybenzenes (such as hydroquinone) are the most common black-and-white developing agents and are quite active to provide development in various black-and-white photographic elements with or without booster and nucleating compounds. However, they are disadvantageous from several technical and environmental considerations. For example, hydroquinone compositions are not completely stable in air, being prone to aerial oxidation. The by-products from instability are often insoluble, black and tarry materials that contaminate the processing solutions and equipment.
The oxidation of hydroquinones also leads to higher pH that in turn leads to increased developer activity. Images can be produced faster so the processing time must be reduced. The net effect is less control of the process, and less desirable sensitometric properties in the processed materials.
In addition, hydroquinones have become an increasing concern from the point of view of potential toxicity and environmental pollution.
Another class of black-and-white developing agents are known in many publications as ascorbic acid and its various derivatives, for example as described in U.S. Pat. No. 5,236,816 (Purol et al). While these types of developing agents are considerably more suitable to the environment, a major concern with ascorbic acid type developing agents is their stability to aerial oxidation. It is well known to improve stability of hydroquinone developing agents by means of various additives, as described in U.S. Pat. No. 4,756,997 (Marchesano), for processing high contrast graphic arts films.
There is a need however for more stable ascorbic acid developing compositions for processing a wide variety of photographic silver halide materials that require a black-and-white developing step.
An improved black-and-white photographic developing composition comprises:
a) an ascorbic acid developing agent,
b) a stabilizing amount of a xcex1-ketocarboxylic acid, and
c) a preservative,
wherein the molar ratio of the xcex1-ketocarboxylic acid to the ascorbic acid developing agent is from about 0.05:1 to about 2.5:1, the molar ratio of the xcex1-ketocarboxylic acid to the preservative is from about 0.05:1 to about 6.25:1, and the composition is essentially free of dihydroxybenzene compounds.
This invention also provides a method of providing an image comprising contacting an imagewise exposed photographic silver halide material with the black-and-white photographic developing composition described above for at least 10 seconds.
This invention also provides a photoprocessing kit comprising the black-and-white developing composition described above, and one or more additional photochemical processing compositions.
The present invention provides a highly stabilized black-and-white developing composition by the use of the xcex1-ketocarboxylic acid as a stabilizing agent, and the specific molar ratios of the xcex1-ketocarboxylic acid to the ascorbic acid developing agent and preservative. This composition is essentially free of dihydroxybenzene compounds, and is preferably also essentially free of alkanolamines.
In addition, the activity of the developing compositions of this invention can be suitably maintained using a replenisher composition that has essentially the same components, concentrations and pH. In effect, the replenisher composition is equally stable as the working composition.
Because the compositions of this invention have increased stability, they can be used as lower replenishment rates during photoprocessing. This would lead to lower effluent volumes and costs. In addition, a certain amount of xcex1-ketocarboxylic acid from the developing step can be carried over into a later processing bath, such as a photographic fixing bath. This xe2x80x9ccarry-overxe2x80x9d xcex1-ketocarboxylic acid may be helpful to reduce sulfur dioxide emissions as described in U.S. Pat. No. 5,629,138 (Faranda et al), and to reduce image dye stain.
The improved stability (that is, reduced aerial oxidation) would generally reduce composition color change. The developing compositions are also xe2x80x9ccleaner workingxe2x80x9d because they require less preservatives (such as sulfites) that create sludge or dirt in the processing bath.